1. Field of Invention
This invention relates generally to packer cups for use in a wellbore, and more specifically, to packer cups that can readily pass over obstructions or burrs on the adjacent interior surface of the well bore or casing strings.
2. Description of Related Art
Packer cups are often used to straddle a perforated zone in a wellbore and divert treating fluid into the formation behind the casing. Using packer cups is desirable since they are simple to install and do not require complex mechanisms or moving parts to position them in the wellbore. Packer cups seal the casing since they are constructed to provide a larger diameter than the casing into which they are placed to provide a slight nominal radial interference with the well bore casing. This interference, “swabbing,” or “squeeze,” initiates a seal to isolate the geologic zone of interest and thereby diverts the treating fluid introduced into the casing into the formation. In many operations, however, the interference or seal between the cup and the casing, or wellbore face, causes abrasive wear on the exterior lip of the cup. Packer cups can suffer damage such as cutting and gouging which occurs as a result of the cup passing through irregularities in a casing such as casing collars and perforation burrs, or by passing through a wellbore restrictions or area of damage. Many packer cup designs have been used. Known cups are generally axisymmetric, ie. having a uniform interior diameter radial distance about the longitudinal axis, and use a steel wire or steel slats to reinforce the cup. Existing cups have a leading edge that is of uniform thickness and uniform interference in the same axial plane. The reinforcing steel wire or slats prevent the rubber in the cup body from extruding when high differential pressure acts on the cup.
Packer cups were developed originally to swab wells to initiate “kick-off” (i.e. start well production). In recent years packer cups or “swab” cups have been used in fracturing or treatment operations carried out on coiled tubing or drill pipe. Such operations require higher pressures and may require multiple sets of packers or isolations across various individual zones. Thus, the demand on the sealing performance of the packer or isolation elements is high and their integrity is critical. Packer or “swab” cups that are capable of withstanding the high differential pressures encountered during fracturing or treatment operations are desired. Furthermore, a cup configuration that is capable of traversing equipment or irregularities in the borehole such as casing collars, perforation burrs, minor restrictions or well bore damage or any other type of well bore obstruction, with minimal cup damage. In known axisymmetric packer cups, the full face or leading edge of the cup encounters such well bore restrictions across its full face, requiring application of a large force to move the cup through the restriction, resulting in significant deformation and possible damage to the cup element. Subsequent to such deformation or damage, the cups may not provide the required seal. A packer or swab cup that can accommodate irregularities in casing or borehole configurations and yet withstand high differential pressures, such as those encountered during fracturing or treatment, is particularly desirable.